Another point that I'd make about finger per fret is that it is not a technique for playing, it is a technique for learning.
like wulf, I can give you probably 20 tunes that I play where there is no discernable left hand technique at all, It is all ad-hoc. That's cool. It doesn't matter how I play it, as long as it sounds good, and I might even deviate from the fpf idea so I can play a note where it sounds a little better. I might not even finger it the same way throughout the song. This is common for a lot of bass grooves. I never had to practice the fingering because the groove was not difficult enough to require concentrating on the fingering.
On the other hand, lets think about transcription or something like playing etudes. My instructor recently assigned me a piece that was written for the classical guitar. It's maybe three pages of music, and I'd like to have it memorized in maybe two weeks. There is a virtual infinity of possible fingerings for a piece of music like this, particularly if I'm not attached to any left hand strategy. But I have a strategy. It's fpf, and rule #1 of fpf is to identity the key signature and choose position accordingly.
So now I have a starting point. Then I practice the first measure of music. If I am already stretching a lot, maybe I should think about changing positions. If I hear a lot of rattles or fret noise, it is usually because I am stretching too much. If everything is cool, I play that measure over and over until I have the 1,2,3,4 committed to memory. Then on to measure two, and so forth, and tomorrow I see how much I've remembered and work on from there.
What I am doing here is training my hand to reproduce a series of motions. Raising or lowering a finger is the simplest of motions. Shifting the hand is also pretty simple, although there's a little more muscle memory involved.
Moving a finger sideways is the most complex motion because it requires fine movements, rotation of the writst and hand, and adjustments in tension. As a result, they're harder to memorize. Also, you'll notice when you're playing a hard piece of music, you get the most flubbed fingerings from the stretches.
The hardest part of learning a challenging piece of music is keeping the set of individual motions in your head and muscles, which you achieve through repetition. To get the repetition going, you have to be able to do the same thing exactly the same way, every time you play it. When you can break a piece of music down into 1 2 3 4s and shifts, stretching the 1 or 4 where necessary, and cheating where you must, you have a much better chance of being able to keep it in memory. But if every time you go repeat a measure, you have to remember which finger it was you used to get a particular note, you're doomed.
I can tell you, as someone who spent years and years trying to transcribe difficult pieces of music, oblivious to the fact that all that stretching and rotating was making things hard, that it is a big waste of time trying to reinvent the wheel, so to speak, of the technique that was established for the guitar and double bass about 300 years ago. What might have cut it when I was trying to learn Higher Ground is not going to cut it when I'm trying to learn the first chorus solo of Giant Steps, because it's a struggle to remember it at all, much less play it at speed.
So anyway, you have to use your head to know when something is not working, but its also foolish to disregard what the masters can teach you about technique. For my money, I'll take Jaco every time
As for the etude, it took about a month of hard practice to get it down, and I still have to play it a couple of times a week to keep it up, but as long as I keep my hands position the way they were when I learned it, the only really tough parts are the stretches
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